I'm sure i've posted my thoughts on these films earlier on in this thread but ages ago...
#1 - I would have to cite 'Alien' as my favorite film + often cite it as my favorite film of all time, even beyond the realm of the Alien franchise. I find everything about this film to be absolutely brilliant. Yes, there are a few 'goofs' but they are easily forgivable. I just find 'Alien' to be a perfect film. A very solid 4 out of 4 stars.
#2 - While i cite 'Alien' as being my favorite movie i really do find 'Aliens' to be just as great but for different reasons. It is without a doubt my favorite action film of all time. Another 4 out of 4 stars.
#3 - Alien 3 (Assembly Cut): A great and often underrated film by non-series fans but then again, i guess our love for it is what helps define us as fans - lol. Again, there are so many things about this film that i love, especially the scenery and the musical score. The theatrical release really cut out many of the moments that make this film what it is - a character piece/human drama. It's pretty easy to see why the public frowned up the theatrical cut after they loved 'Aliens' so much. Of course they likely would have hated the Assembly Cut just as much @ the time, considering the drastic differences in style/tone. A nice 3.5 out of 4 stars.
#4 - Alien Resurrection: the sore thumb of the lot. I don't hate this film by any means but i do feel it pales in quality to the original 3 films. The style/tone the film takes on is very much in contrast with the previous films. Plus Ripley is now Ripley 8 + the Aliens were no longer scary. As a sci-fi flick it's really not that bad + certainly enjoyable for the action + even the characters aren't so bad after several viewings - lol. Still, not up too par with the rest of the lot. A mediocre 2 out of 4 stars.
That's pretty much it. I could ramble on more about each but who would read it? - lol.